1. Field of the Invention
This invention relates generally to the field of actuation systems, and more particularly to a pneumatic/mechanical robotic-system actuator. Specifically, this actuation system provides efficient and direct chemical (fuel) to mechanical energy conversion using a combined internal-combustion free-piston or piston-crank engine-air compressor to generate pressurized air as a working fluid. The invention further relates to an autonomous power supply that can support actuation function for long periods of time using only chemical energy. As in a Brayton-cycle, this is fed through lean-burn catalytic reactors into a drive turbine to operate a ball-screw push rod mechanism. The resultant actuator is thermodynamically efficient, providing significant force in addition to rapid, precise, and large-displacement motion.
2. Description of Prior Art
Actuators are used in many mechanical systems to produce motion. The primary types include hydraulic, pneumatic, and electric motor driven systems. These systems are designed to provide motive force, rapid motion (with high frequency bandwidth response) and precise positioning. At the same time such systems must not sacrifice too much energy or consume too much working fluid. Another desired attribute is the ability to produce high power output from a small, compact package, i.e. having high energy-density. While the above qualities and benefits are needed in actuation systems, the technology used dictates the limits and compromises of each system with respect to providing all the features. Generally, a system will provide the advantages of some, but not all, desired features. No prior actuation system has been able to operate on compressed air provided by a small fuel-efficient internal combustion engine-compressor. To date compressed air systems could not simultaneously provide rapid response, low fuel consumption, low working fluid loss, and significant output force. A significant problem of Brayton-cycle machine is the continuous high temperature that quickly erodes components.
Prior technologies include pneumatic (compressed air) systems, hydraulic systems, and electromechanical systems.
The prior technologies are deficient in certain critical functions. The pneumatic system except when very high pressures are used is typically a poor performer in the areas of stiffness, of providing high bandwidth, and of maintaining position accuracy. The hydraulic system has a problem with high consumption of working fluid while providing both large-displacement motion and high force. The electromechanical systems are most common. These become excessively large and complex because of heavy batteries if designed to generate both a high force and rapid motion. Electrical batteries are present in a large number of forms. For this application, batteries would provide adequate performance for approximately 20-30 minutes. They would then be recharged or discarded. FIG. 1 is a prior art continuous-combustion gas turbine known also as a Brayton-cycle gas turbine. A combustible fuel, such as gasoline, is provided via input 10 to a burner 12 which ignites the fuel by mixing it with compressed air from an air compressor 14 in manifold 13. After fuel ignition burning and mixing high temperature gases are allowed to exit via nozzles 16. As is well known nozzles provide areas where gas pressure is decreased and velocity increased. After passing through nozzles 16 high velocity gas turns a turbine wheel 18 which in turn drives a load via shaft 20. Spent gas is vented via exhaust 22.
A Brayton-cycle machine is thus built using a compressor to feed air under pressure to an air transfer manifold 13. The bypass air flow mixing and combustion chamber burning permits a constant pressure heat addition. The addition of heat energy to the cycle at a constant pressure is the unique feature that characterizes the Brayton-cycle process. This process may include flow mixing between bypass air and combustor outlet air. The expansion process uses turbine 18 as the energy extractor. Exhaust 22 constitutes constant pressure heat removal. Because of the desired constant high temperature heat addition in manifold 13, the related components burner 12, manifold 13, nozzles 16, and turbine wheel 18 quickly erode.
The primary object of the present invention is an actuator with efficient conversion of chemical (fuel) into mechanical energy in the form of compressed air that generates a force to move objects without high temperature erosion problems for working components.
Another object of the invention is an actuator providing precise movement.
Another object of the invention is an actuator with large-displacement motion.
A further object of the invention is an actuator producing rapid motion.
Yet another object of the invention is an actuator providing conversion of energy from fuel into compressed air using an integrated free-piston or piston-crank internal combustion engine-air compressor.
A final object of the invention is to provide an actuator with high-energy density that offers compact packaging and high power output.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
The machine described is for generating actuation force with rapid, precise, and large-displacement motion comprising: an internal combustion engine-air compressor energy source, a pneumatic working fluid, two high pressure burners, two control valves, a reversible turbine, a speed-reducing transmission, a ball-screw push-rod mechanism, an optical encoder and a control system.
Like a Brayton-cycle machine it uses two high-pressure burners coupled to a reversible-drive turbine and transmission to generate large-displacements with precise positioning using a ball-screw push rod.
Each of these relates to the present system; offering forms of energy transfer based on working fluid or mechanical drive to develop controlled forces. The present system emulates a hydraulic actuator in that it is capable of producing large-displacement motion and significant force. It relates to the pneumatic system in that the working fluid is compressed air. It is similar to the electro-mechanical actuator in that it uses a stiff output gear train and ball-screw push rod to generate force.